1. Field of the Invention
The present invention relates in general to an injection molding system. More particularly, the present invention relates to an improved injection molding apparatus characterized in particular by a valve actuated assembly that utilizes a flow insert for facilitating annular melt flow about the valve pin.
2. Discussion of the Related Art
Valve actuated injection molding nozzles are used to keep the melt at process temperature between the extruder nozzle and the gate, and also used to actuate a valve pin that opens and closes the gate. In the closed position, the valve forms a seal to stop melt from flowing into the cavity, while in the open position the valve is retracted away from the gate of the cavity and melt flow into the cavity is permitted.
A problem with valve gated injection molding is that when the valve is open the melt flows about the valve pin and a "dead" spot can be created behind the valve pin. A dead spot is an area where the melt is not flowing at the same rate as the surrounding melt flow. The presence of a dead spot leads to some of the melt being exposed to the heat from the heated nozzle longer than the rest of the melt. Consequently, the melt from the dead spot can degrade more than the rest of the melt, and have a different coloration, consistency, and temperature than the rest of the melt. This can cause streaks to appear in the finished plastic article. Furthermore, the slow moving melt in the dead spot can mix with a new color when the user wishes to change color. This requires greater time to clean out the old color before articles having the new color can be made without streaks of the old color appearing in the article.
An additional problem is created when the melt flow is directed about the valve pin. The valve pin tends to interrupt or separate the flow of the melt traveling to the gate. The melt, however, often will not properly recombine at the gate after it is separated by the valve pin, causing weld lines to appear in the plastic article.
Another problem with valve gated assemblies is the force used to actuate the valve. Actuators often are required to exert a great deal of force to open and close the valve, due to the frictional forces involved. Often, the forces exerted by the actuator are transmitted unnecessarily in a direction different from the direction that the valve pin is traveling, due to poor design of the valve pin actuator assembly. Consequently, these forces wear on and reduce the life of the actuator and the valve pin assembly.
In view of the foregoing, it is object of the present invention to provide an injection molding system having an improved melt flow direction about the valve pin, that eliminates dead spots in the melt flow.
It is a further object of the invention to provide an injection molding system having an improved melt flow direction about the valve pin that eliminates weld lines caused by interruption of the melt flow by the valve pin.
It is a further object of the invention to provide an actuator apparatus that transmits forces to the valve pin actuator in the direction the valve pin is moving, without creating frictional force components normal to the movement of the valve pin.